The invention relates to using brazing to assemble together thermostructural composite materials, and in particular ceramic matrix composite (CMC) materials. CMC materials are typically formed by a porous substrate, such as a porous fiber substrate, that has been densified by a ceramic matrix. The fibers of the substrate may be made of carbon or of ceramic. By way of example, the matrix may be made of a refractory ceramic such as a refractory carbide, nitride, boride, or oxide. CMC materials, such as for example C/SiC composite materials (carbon fiber reinforcement with a silicon carbide matrix), are remarkable for their mechanical properties, which make them suitable for constituting structural elements, and for their ability to conserve those properties at high temperatures.
When making structures out of ceramic matrix composite materials, it is common to construct them from independent elements made of CMC materials, which elements are assembled together by brazing. Nevertheless, brazing ceramic matrix composite materials together is technically difficult, and the breaking stress of the brazed joint is often insufficient relative to the forces to which the assembly might be subjected, in particular shear forces.
Pieces made of CMC materials present a high degree of surface roughness, which prevents the brazing composition spreading well in the zone where the brazed joint is formed, thereby creating zones of weakness in the brazed connection.
Also, while the brazing composition is diffusing between the assembly faces of the parts to be brazed together, gas is given off due to reactions between the brazing composition and the ceramic particles used for conveying the brazing composition by capillarity between the assembly faces. Some of that gas becomes imprisoned inside the brazed joint, thereby leading to a brazed joint that is porous, and in which there remain local braze-free areas between the two surfaces. That lack of material leads to defects in the connection between the two parts, and consequently degrades the quality of the assembly by weakening the connection that is made.